Compensation valve arrangements regulate flow through a directional valve arrangement between a supply port and one or more work ports. Such valve arrangements may be used to actuate hydraulic drives (e.g., hydraulic cylinders, hydraulic motors, etc.) in working machines, vehicles, or other hydraulically-operated systems. For example, in a backhoe, a first hydraulic drive can be used to tilt a beam in relation to a chassis; a second hydraulic drive can be used to tilt an arm in relation to the beam; a third hydraulic drive can be used to activate a shovel; and a fourth hydraulic drive can be provided to turn the upper vehicle body in relation to the lower vehicle body.
In general, compensation arrangements are provided in load sensing valves to maintain constant pressure drop across a metering orifice created by spool movement. Accordingly, the flow of the hydraulic fluid from the supply channel arrangement to the connected hydraulic drive depends on the opening degree of the directional valve arrangement. Thus, a practically proportional function of the directional valve arrangement is obtained.
Some types of compensation valve arrangements have the compensator located upstream of the metering orifice. These types of compensation valve arrangements are referred to as “pre-compensation valve arrangements.” Pre-compensation valve arrangements are configured to sense the pressure at an individual work port and to compare the sensed work port pressure against the pressure at an outlet of the compensator (i.e., the compensated pressure). During flow saturation (i.e., when the demand is greater than the pump is supplying), the pre-compensation valve arrangement gives priority to lower load drive. However, the pre-compensation valve arrangement slows or even stops higher load drive.
Some types of compensation valve arrangements have the compensator located downstream of the metering orifice. These types of compensation valve arrangements are referred to as “post-compensation valve arrangements.” Post-compensation valve arrangements are configured to sense the highest pressure of all of the work ports and to compare the sensed pressure against the pressure at an inlet of the compensator. During flow saturation, the post-compensation valve arrangement proportionally reduces the speed of all drives connected to the system per the opening of the metering orifices. The post-compensation arrangement does not stop the highest load drive. However, the post-compensation valve arrangement does not provide priority to any of the drives.